Method of recording seismic data



March 7, 1967 c.w. Boss ETAL METHOD OF RECORDING SEISMIC DATA Original Filed Dec. 16, 1963 FIG. 3-

4 FROM 25 CYCLE BREADTH GALVANOMETER 5 FROM I3 AMPLITUDE GALVANOMETER COLOR RECORDING TRANSPARENT COLORS LIGHT SOURCE .[TL u ELECTRIC'AL A MPLIFIER CYCLE BREADTH GALVANOMETER SIGNAL FR om AMPL/IFIER l3 SWITCH LIMITER RECORDER AMPLIFIERS AMPLITUDE e ALVA NOME "re R GEOPHONES 2 HOT POINT Fl INVENTOR.

ROB E RT F. GREGORY,

BY HARL REFLECTING SURF ACE 7W. BOGS,

ATTORNEY.

United States Patent 3,308,472 1 METHOD OF RECORDING SEISMIC DAT Charles W. Bogs, Houston, Tex., and Robert F. Gregory, Denver, Colo., assignors to Esso Production Research Company Original application Dec. 16, 1963, Ser. No. 331,027, now Patent No. 3,241,150, dated Mar. 15, 1966. Divided and this application June 1, 1965, Ser. No. 473,260 2 Claims. (Cl. 346-1) This is a division of application Ser. No. 331,027, filed Dec. 16, 1963, nowPatent No. 3,241,150.

The present invention relates generally to the display of electrical transients. In particular, it concern-s the presentation of seismic data in which both the cycle breadth and amplitude parameters of a seismic signal are simultaneously recorded photographically. The cycle breadth information is presented in different colors which correspond to different lengths of cycle breadth and the amplitude information is presented in variable area.

As is well known in geophysical prospecting, a seismic shock is imparted to the earth generally by means of an explosion and seismic waves generated by the explosion travel downwardly through the subsurface and are reflected back to the surface by subterranean strata. These waves are detected at spaced points on the earths surface which are at selected distances from the explosion point, termed the shock point. The depth of subsurface reflecting strata can be determined by measuring the time intervals between initiation of the explosion and detection of the reflected waves at the detection points. Various corrections may be made to adjust the arrival times of the reflected waves to compensate, for example, for differences in elevation of the shock point and the various detecting points, and to compensate for the low velocity layer of the earth at the several points.

Amplitude, frequency, total energy, and other parameters of the seismic signals aid observers in determining the characteristics of subsurface structures. Also, various techniques have been used to present the signals in forms that are easier to analyze. One such technique is the display of the signals in variable density or variable color where the signals are reproduced as photographic traces which vary in intensity in proportion to variations in amplitude or frequency or some other parameter of the signals.

The photographic technique is used in the present invention to present two parameter-s of the seismic signal, cycle breadth and amplitude, together. The combination of these two parameters results in a display in which the colors of recorded blocks change with cycle breadth variation and the size of the area occupied by each color block varies with amplitude. The selection of the colors, their number and intensity, is arbitrary. The units of cycle breadth that each color represents also is arbitrary.

The record made in accordance with the teachings of the invention presents frequency and cycle breadth information better than they have been presented heretofore. Undesir-able, low amplitude noise, characteristic of cycle breadth information, is eliminated permitting the observer to interpret and analyze better the seismic signals in order to gain information as to the nature of the subsurface formations such as porosity, bed thickness, slope, velocity, etc.

Briefly, the invention comprises -a method for recording a seismic signal as a photographic trace, the color of which varies in accordance with changes in cycle breadth and the area of which varies with amplitude of the seismic signal. The apparatus of the invention and its operation is as follows. Two separate, moving coil galvanometers, one of which pivots in response to cycle breadth voltage and the other of which pivots in response to amplitude voltage of the seismic signal are both focused on a while light source and adjusted to impinge overlayed images of this light source on a common area of color-sensitive film which is mounted on a rotatable drum. As array of different, transparent colors which form a mask are placed between the light source and the cycle breadth galvanometer in a manner such that changes in the cycle breadth voltages produce variations in the color of the light projected to the color film. An opaque strip provided with a narrow, transparent slit is positioned between the light source and the amplitude galvanometer in a manner such that at zero voltage a beam of clear, white light is focused to impinge on the film. The color mask may be of the type described in US. patent application Ser. No. 136,- 581, entitled Recording Mode and Apparatus for Seismic Data, filed Sept. 7, 1961, by W. A. Alexander.

A primary object, then, of the present invention is to provide an improved method and apparatus for displaying seismic signal, cycle breadth, and amplitude information. A further object of the present invention is to provide an improved method and apparatus for displaying seismic signal cycle breadth information which eliminates low amplitude noise.

The term frequency as used herein means the number of times a signal wave form or seismic signal crosses the zero signal axis per unit of time. The term positive zero crossing means the crossing of a Zero signal axis by the signal wave form when the wave form changes from negative to positive and negative zero crossing means the point where the seismic signal crosses the zero signal axis and changes from a positive to a negative value. The term half cycle breadth means the distance representative of time between any two negative-positive or positivenegative successive zero crossings. The term full cycle breadth means the distance representative of time between two successive, positive zero crossings, or two successive, negative zero crossings.

The circuit for producing the half cycle breadth signal is the same as the one described in US. patent application Ser. No. 227,284, entitled Seismic Presentation by K. O. Heintz. The present invention combines two of these half cycle breadth circuits to produce the full cycle breadth signal.

The above object and other objects as well as the advantages of the invention will be apparent from the following, more detailed description thereof when taken with the drawings wherein:

FIG. 1 is a schematic representation of a profile of the earths subsurface illustrating the manner in which the original signals are obtained;

FIG. 2 is a schematic illustration of the electrical circuits used to form the cycle breadth signal and to transmit both the amplitude and cycle breadth signals to their respective galvanometers;

FIG. 3 is a schematic representation of the optical system for recording the signals.

In FIG. 1 there is shown a reflecting subsurface 10, a shot point 11, and surface pickups or geophones 12. The geophones or transducers 12 translate the reflected shock waves resulting from the explosion at shock point 11 into electrical signals representative of the seismic waves. The electrical signals are amplified by amplifiers 13 and recorded as indicated at 14.

Referring to FIG. 2, the amplified electrical signals produced by the reflected shock waves resulting from the explosion at the shock point are fed to a cycle breadth detector circuit generally designated 15. The operation of the cycle breadth detector shown in the block diagram of FIG. 2 is as follows. The amplified seismic input signal 16 is clipped in the limiter 17, and the squared voltage signal 16a is fed to identical shaping circuits 15a and 15b. The signal sent to circuit 15b is first inverted 3 by inverter 18 as indicated at 16/). In circuit a, square wave 16a builds up a charge in a capacitor 19 during one-half cycle of the seismic signal which is held during the other half of the cycle as seen at 1% by the capacitor 19 and is discharged by a pulse 20a from the difierentiator 20 at the Zero crossing time preceding the next cycle. This voltage is transferred by the voltage follower 21 which has a very high input impedance so that it does not discharge capacitor 19 to the electronic switch 22. In order to make use of the other half of the seismic signal, the inverted square wave 16b is passed through circuit 15b in the same manner that square wave 16a was passed through circuit 15a before being fed into electronic switch 22. This switch is alternately switched from the output of voltage follower 21 to the outputof voltage follower 23 of network 15]) by the square waves 19a and 24a. The output signal 25a from the electronic .switch 22 represents the cycle breadth of the seismic signal in positive going pulses with respect to zero signal level. This signal is amplified by amplifier 25 and impedance matched to drive the cycle breadth galvanometer 30. The amplitude voltage is fed directly to the amplitude galvanometer 31 from amplifier 13 as shown.

Referring to FIG. 3, the cycle breadth voltage which varies with cycle breadth and the amplitude voltage which varies with amplitude are supplied to the separate moving coil galvanorneters 3i) and 31, respectively, which galvanometers are both focused on a white light source 35 and adjusted to impinge overlaid images of this light source on a common area of color film through a condensing lens 36 which focuses the light from the galvanometers. The film is affixed to a drum 37 which is moving at constant speed in respect to the magnetically recorded informationthat is being analyzed.

An array of different, transparent colors 40' (stacked mask) are placed between the light source and the cycle breadth galvanometer in a manner such that changes in cycle breadth voltage will produce changes in the color of light striking the color film in blocks. An opaque strip 41 with a single narrow transparent slit 4?. is positioned between the amplitude galvanometer 31 and light source in a manner such that at Zero voltage, no signal, a beam of clear white light is impinged on the film of such an intensity as to wipe out the colored lights supplied by the cycle breadth galvanometer 30. With increases in amplitude voltage, the amplitude galvanometer 31 is moved away from the clear slit and diminishing amounts of white light are mixed with the colored light from the cycle breadth galvanometer 3i At maximum amplitude no white light is impinged by the amplitude galvanometer on the film and a clear color, undiluted by white light supplied by the cycle breadth galvanometer 30 is recorded.

The recording method was described herein as a single, photographic trace recording; however, this method is readily adapted to multiple channel recording by providing suitable shielding for each separate channel. US. Patent No. 3,011,856, entitled Automatic Plotter, issued Dec. 5, 1961, to C. C. Palmer and R. R. Briscoe shows and describes apparatus for channeling separate traces that would be suitable for this purpose.

Having described the method, apparatus, objects and advantages of the invention, we claim:

1. A method for recording seismic signals as photographic traces comprising varying the color of a photographic trace in proportion to variation in the cycle breadth of seismic signals while simultaneously varying the area of the trace in response to variations in amplitude of the seismic signal, said trace decreasing in area with decreasing amplitude and vice versa.

2. A method for recording seismic signals as photographic traces comprising projecting onto a lightsensitive medium, light in colors which vary in response to variations in the cycle breadth of seismic signals and simultaneously overlaying said color image with white light by projecting white light onto said light-sensitive medium which white light decreases in intensity in response to increases in amplitude of the seismic signals whereby the area occupied by said color is increased and decreased in response to variations in amplitude of said seismic signals.

No references cited.

RICHARD B. WILKINSON,Primar-y Examiner.

L. M. LORCH, Assistant Examiner. 

2. A METHOD FOR RECORDING SEISMIC SIGNALS AS PHOTOGRAPHIC TRACES COMPRISING PROJECTING ONTO A LIGHT-SENSITIVE MEDIUM, LIGHT IN COLORS WHICH VARY IN RESPONSE TO VARIATIONS IN THE CYCLE BREADTH OF SEISMIC SIGNALS AND SIMULTANEOUSLY OVERLAYING SAID COLOR IMAGE WITH WHITE LIGHT BY PROJECTING WHITE LIGHT ONTO SAID LIGHT-SENSITIVE MEDIUM WHICH WHITE LIGHT DECREASES IN INTENSITY IN RESPONSE TO INCREASES IN AMPLITUDE OF THE SEISMIC SIGNALS WHEREBY 